1. Field of the Invention
The present invention relates to a method for forming images by image intensifying, more particularly, to a method for forming images by image intensifying minimizing undesired variations in photographic properties (fog, sensitometric gradation, maximum density of colored images, etc.) due to catalytic nuclei poisoning. In addition, the present invention relates to a method for forming images in which a reduction of the intensifying effect is prevented and fog is minimizee. One characteristic of the present invention is to provide a method for forming images by an intensifying treatment utilizing a photographic element comprising an image-forming unit layer using light sensitive silver halide in a smaller amount than the stoichiometric amount, based on color former, in combination with a sufficient amount of color former.
2. Description of the Prior Art
Various methods for intensifying the formation of images by subjecting a silver halide light-sensitive material to intensifying upon development are known.
The formation of dyes by a process which comprises oxidation of a p-phenylene-diamine color developing agent due to decomposition of hydrogen peroxide on a silver catalyst in the presence of a color former, followed by coupling with the color former (this phenomenon is referred to as "color intensification") is described in, for example, Friedman, History of Color Photography 2nd edition, page 406 (1956). Further, with regard to other various photographic techniques utilizing decomposition of peroxides on the surface of a noble metal, there are descriptions in German Patent Applications (OLS) Nos. 1,813,920, 1,950,102, 1,955,901, 1,961,029, 2,044,833, 2,044,993, 2,056,360, 2,056,359 and 2,120,091, etc. On the other hand, it has been known for a considerable time that peroxides are decomposed on the surface of a noble metal. For instance, many examples thereof are described in Shokubai Kaguka Koza (Lectures of Catalyst Technology), volume 2 (1966) published by Chijin Shokan, Tokyo.
Furthermore, with respect to color intensifying using a cobalt complex on the surface of a noble metal, there are descriptions in, for example, Japanese Patent Applications (OPI) Nos. 9728/73, 9729/73, 48130/73, 84229/74, 84239/74, 84240/74, 97614/74, 102340/74, 102341/74, etc.
Further, a color intensifying method using halogenous acids such as chlorites or the like is described in Japanese Patent Applications Nos. 128,237/74 and 139917/74.
These intensifying methods can be facilitated using conventional silver halide light sensitive materials, in particular, low silver type light sensitive materials or the likes as are described in Japanese Patent Application (OPI) No. 9728/73. That is, these methods form dyes due to a coupling reaction of the oxidation product of a color developing agent caused by a reduction of silver halide with a color former, which are particularly characterized in that the amount of silver is greatly reduced.
In these three intensifying methods, the intensifying methods which use halogenous acids and the method which uses peroxides are preferred because of the high intensifying activity as compared to the intensifying method using a cobalt (III) complex compound as is described in the aforementioned Japanese Patent Application (OPI) 9728/73, etc.
However, halogeneous acids or peroxides, due to their strong oxidation capability, tend to oxidize a reducing agent (for example, a color developing agent, etc.) even at areas other than image areas composed of metal silver during the intensifying and form dyes by reacting the oxidation product with the color former (for example, coupling reaction, etc.) so that fog is liable to form. Such formation of fog is conceivably also suggested by the description with regard to the decomposition of peroxides, appearing in, for example, W.C. Schumb, et al., Hydrogen Peroxide, page 590 (1955), etc.
On the other hand, there is the defect in intensifying processes using highly active halogenous acids or peroxides that the intensifying effect tends to be restrained by various compounds which can be present during the intensifying process, e.g., compounds which are carried from a developing bath (e.g., potassium iodide, etc.), additives incorporated in the light-sensitive material, etc.
Such a restraint of the intensifying effect could also be expected from the fact that decomposition of peroxides on a noble metal, heretofore known, is poisoned by various compounds or ions. For example, it is described in Shokubai Kogaku Koza (Lectures of Catalyst Technology), Volume 2, pages 272-296 (1966) published by Chijin Shokan, Tokyo, that H.sub.2 S, HCN, HgCl.sub.2, Hg(CN).sub.2, I.sub.2, NH.sub.2 OH, C.sub.6 H.sub.5 NH.sub.2, etc., are such (catalyst) poisons. These compounds restrain the intensification of metal silver and the like on a catalyst by not only peroxides but also by halogenous acids.
In addition, the intensifying effect of halogenous acids or peroxides is inhibited in a process of developing a silver halide photographic light-sensitive material; this might be because bromine ions or iodine ions in a silver halide are released and the released ions are absorbed on the surface of the developed silver so that the catalytic nuclei are thereby poisoned. Further, in most cases, bromine ions are added in an amount of from 0.1 g/liter to 10 g/liter to a developer for anti-fogging, hardening, maintaining the activity of a continuously used liquid constant, etc., and are carried into an intensifying bath to poison the catalytic nuclei. The oxidation of a reducing agent (for example, a color developing agent, etc.) with an intensifying agent on the thus poisoned catalyst is strongly restrained, and, therefore, the intensifying effect is inhibited.
These compounds having an intensifying effect, such as peroxides, halogenous acids, cobalt (III) complex compounds and the like, are referred to as an intensifying agent; and peroxides halogenous acids and the like which possess a higher activity than cobalt (III) complex compounds are referred to as highly active intensifying agents. A processing bath containing an intensifying agent is referred to as an intensifying bath.
On the other hand, as mentioned hereinabove, a highly active intensifying agent (for example, peroxides, halogenous acids, etc.) is liable to cause fog, especially at non-image areas, and it is thus conceivable one could prevent fog by having an anti-fogging agent present in a process where a reducing agent (for example, a color reducing agent, etc.) is oxidized with such a highly active intensifying agent on a catalyst. However, in this case, not all known anti-fogging agents are effective, and effective ones are limited to those having specific chemical structures. Furthermore, if a compound having such an anti-fogging effect coexits in the system, the poisoning effect due to a compound which would poison catalyst nuclei as mentioned above in particularly strongly exibited, as compared to the case where no anti-fogging agent is present. As a result, the intensifying effect is remarkably inhibited.